Electrostatic precipitator and gas sampling system

ABSTRACT

An electrostatic precipitator especially suited for use in a gas sampling system for removing solid particulate material from a sample gas stream withdrawn from an ore reduction roaster for passage to a gas chromatography unit is designed to remove residual and very small particulate material from such a gas stream after such a stream has first passed through a relatively coarse screen filter. The electrostatic precipitator includes a housing divided by a downwardly extending partition into an ionization chamber containing an ionizing wire electrode and a collector chamber containing a plate-type collector electrode. The partition terminates upwardly of the floor of the housing to provide a dust-collection chamber through which the gas stream flows on passing from the ionization chamber to the collector chamber. In the overall gas sampling system, a blow-back gas system is provided for dislodging solid material from the screen filter and from the upstream portion of the sampling conduit and for returning dislodged material to the roaster to prevent cumulative plugging of the system. Operation of such a blow-back system is usefully controlled by a sampling programmer of the gas chromatography unit to which the system is coupled so that such blow-back system operates automatically between successive analyses.

United States Patent Vaneldik et al. Dec, 12, 1972 [54] ELECTROSTATIC PRECIPITATOR :avitz enne D GAS SAMPLING SYSTEM- 3,041,869 7/1962 Spackl er et a1 ..73/23.1 [72] 'Inventors: Jan Frederik Vaneldik, Edmonton, 3,176,501 4/1965 Briggs ..73/23.1

Alberta; Ronald lan Wilson, Sherwood Park, Alberta; Gerrit Richard FOREIGN PATENTS OR APPLICATIONS Kampjes; William James Lavender, 230,330 4/1960 Australia ..55/155 both of Edmonton, Alberta all of 945,167 11/1948 France ..55/146 Canada 627,068 7/1949 -Great Britain.... ..55/136 1,183,617 3/1970 Great Britain ..55/386 [73] Assignee: Sherritt Gordon Mines Limited,

Toronto, Ontario, Canada Primary Examiner-Dennis E. Talbert, Jr. [22] Filed: Aug. 4, 1970 Atto n y-Frank l. Piper, Arnie l. Pots and James T.

W1lbur [21] Appl. No.: 60,785

. [57] ABSTRACT [52] US. Cl. ..55/120, 55/126, 55/ 138, An electrostatic precipitator especially suited for use 55/141, 55/145, 55/ 146, 55/ 149, 55/ 151, in a gas sampling system for removing solid particulate 55/154, 55/270, 55/283, 55/302, 55/316, material from a sample gas stream withdrawn from an 55/342 55/335 55/3 55/417 5 5/41 ore reduction roaster for passage to a gas chromatog- 55/465, 55/5 3, 73/231 73/4215 174 1 R raphy unit 1s deslgned to remove resrdual and very [51] 1m. (:1 ..B03c 3/01 small Partwulate material from h a gas stream after [58 Field or Search ..55/101, 124, 126, 127, 128, such a streamfhas p through a r e y 55/129, 1 5 52 13 8 .1 2113122i ifiiiidghvaefiwi fiiffitvrfihi gltflfsli partition into an ionization chamber containing an 283, 120, 141, 145, 149, 154, 316, 342, 385, ionizing wire electrode and a collector chamber con- 417,418,466, 503; 73/23.l, 421.5; 174 15 taining a plate-type collector electrode. The partition BB, 16 terminates upwardly of the floor of the housing to provide a dust-collection chamber through which the gas [56] References C'ted stream flows on passing from the ionization chamber UNITED STATES PATENTS to the collegtlor clhanliber. In the overall gas sgncilplifng system, a owac gas system 1s prov1 e or 3,408,793 11/1968 Frazer ..55/197 dislodging solid material from the screen filter and 3,422,665 l/1969 Haase ..5 5/67 X from the upstream portion of the sampling conduit 3,457,787 7/1969 Maatsch et al. ..'..73/421.5 and for returning dislodged material to the roaster to 3,615,256 10/1971 Miller ..23/288 S prevent cumulative plugging of the system. Operation Dav1dson X of uch a blow back ystem is usefully controlled a 1,264,674 4/1918 Moller ..174/315 x Sampling programme, of the gas chromatography unit 'gl "SS/137 X to which the system is coupled so that such blow-back 6 5 6/1930 5: system operates automatically between successive 1,790,961 2/1931 Welch..... analyses' 2,443,662 t 6/1948 Pegg ..55/138 1 Claim, 5 Drawing Figures 2,556,832 6/1951 Y .v

PATENTEnnEc 12 w I 3 705,478

SHEET 2 BF 2 INVENTORs: J. F. VANELDIK 59 R. 1. WILSON e. R. KAMPJES B Y 5' 54 5 I W. J. LAVENDER FIGS 1. ELECTROSTATIC PRECIPITATOR AND GAS SAMPLING SYSTEM v The present invention relates to electrostatic precipitators and more particularly to electrostatic precipitators especially suited for use in gas sampling systems for the removal of finely divided solid particulate material from gas sample streams withdrawn from ore reduction roasters for analysis in gas chromatography units. r

Inore reduction roasters, it is customary to heat the ore charge in the roaster with the hot gases from oil burners or the like which areoperated with a deficiency of air to provide the necessary reducing conditions in the roaster. Consequently, the gases present within the roaster are charged fairly heavily with dust and soot and, if the composition of the gas is to be analyzed by gas chromatography, it is necessary first to remove solid particulate material from the gas sample prior to its pasags t .the gas chromatography unit.

in the absence of such prior cleaning of the gas sample stream, the automatic sampling, division and calibration valves, as well as the sampling loop tubing of a gas chromatography unit rapidly have solid material deposited therein and proper operation of the gas chromatography unit is not then obtained. Furthermore, if such a sample gas stream is passed directly from an ore reduction roaster to a gas chromatography unit, the transfer conduit provided for this purpose eventually becomes plugged and prevents effective operation of the analysis system.

Although it is possible to restrict the extent to which solid particulate material in a sample gas stream passes to a gas chromatography unit from an ore reduction roaster by providing appropriate filters in the sampling conduit, there are still many serious difficulties. For example, dirt and soot will still settle in the sampling conduit upstream of the filterand will eventually cause blockage;

Furthermore, a suitable filter for this purpose must be fine enough to remove a major proportion of the solid particulate material yet such a filter will rapidly become blocked by particulate material. With coarser filters, inadequate particle retention on the filter screen results in the gaschromatography' unit itself rapidly becoming tightly packed with dust.

It is accordingly a principal object of this invention to provide a gas sampling system for removing solid particulate material from a sample gas stream from an ore reduction roaster for subsequent passage to a gas chromatography unit for analysis therein and which sampling system is free of the aforementioned disadvantages. p

More particularly, it is an important object of this invention to provide a gas sampling system for the aforementioned purpose and by the use of which system essentially all solid particulate material and including particles as small as 0.01 microns and less are removed from a gas sample stream prior to the passage of such stream to a gas chromatography unit.

A further object of this invention is to provide a gas sampling system in which means are provided for preventing or reversing the cumulative deposition of particulate material within the system.

Yet another object of this invention is to provide a novel electrostatic precipitator which is. especially suited for use in the gas sampling system of the invention.

Another object of this invention is to provide a gas sampling system in which the total duration for the passage of a gas sample through the system, for example, from an ore reduction roaster to a gas chromatography unit, is relatively short.

Other objects of the invention will become apparent as the description herein proceeds.

In its broadest scope, the present invention provides a gas sampling system for the removal of solid particles from a gas stream sampled from an ore reduction roaster for passage to a gas chromatography analysis unit, which-system includes a sampling line adapted to be connected to the ore reduction roaster for the passage through said sampling line of a gas stream; laden with both coarse and finely divided solid particles, a screen filter in said sampling line for the passage of said gas stream therethrough for the removal of coarse solid particles from said gas stream by, said filter; an electrostatic precipitator-for the removal of finely divided solid particles from said gas stream flowing through said screen filter; a transfer line interconnecting said screen filter and said electrostatic precipitator for the passage of a gas stream from said screen filter, after the removal of coarse solid particles therefrom by said screen filter, to said electrostatic precipitator; gas outlet means extending from said electrostatic precipitator for the flow of a gas stream therefrom, after theremoval of said finely divided solid particles from such a gas stream in said electrostatic precipitator; first valve means operatively associated with said transfer line for movement between open and closed positions for controlling the flow of a gas stream through said transfer line to said electrostatic precipitator; a gas supply line in gaseous communication with said transfer line for the introductioninto said transfer line of a blow-back gas, and second valve means operatively associated with said gas supply line for movement between open and closed positions for permitting the flow of blow-back gas when in said open position thereof through said gas supply line into said transfer line and, when in said closed position thereof, for preventing the flow of said gas stream from said screen filter into said gas supply line; whereby said gas sampling system may be used with said first valve means in said open position thereof and with said second valve means in said closed position thereof to remove both coarse and finely divided solid particles from a gas stream sampled from an ore reduction roaster and to supply the resultingly cleaned gas stream through said gas outlet means to a gas chromatography unit, and whereby a blow-back gas may be introduced into said system through said gas supply line with said second valve means in said open position thereof and with said first valve means in said closed position thereof to cause a reverse flow of gas through a part of said transfer line to said screen filter and then through said sampling line to dislodge solid particles from within said transfer and sampling lines, and from said screen filter and to return resultingly dislodged material to said ore reduction roaster.

As already indicated, this invention also provides a novel electrostatic precipitator especially suited for use in a gas sampling system as hereinbefore defined. Such an electrostatic precipitator can broadly be defined as comprising a .closed housing with electrically conductive side walls and internally divided into separate ionization collector chambers; a gas inlet communicating with said ionization chamber for the passage of gas stream into said ionization chamber; a gas outlet communicating with said collector chamber for the passage of a gas stream outwardly from said collector chamber; an ionization electrode mounted in said ionization chamber on electrically insulating support means; a collector electrode mounted in said collector chamber on electrically insulating support 'means; high voltage electrical supply means electrically connected to said ionization and collector electrodes for the application thereto of a high electrical voltage relative to said electrically conductive side walls of said housing whereby electrical discharge from said ionization electrode causes solid particles in a gas stream flowing through said ionization chamber to become electrically charged and electrically charged solid particles present in said gas stream flowing through said collector chamber are attracted to and collected on one of said collector elec trodes and said electrically conductive side walls of said housing.

Other features and advantages of the invention will become apparent as the description herein proceeds.

The invention will now be described with reference to the accompanying drawings showing preferred embodiments of the invention in which:

FIG. 1 is a schematic illustration of one embodiment of a gas sampling system in accordance with the present invention showing the gas sampling system coupled to an ore reduction roaster and intended for supplying gas samples removed from the roaster to a gas chromatography unit, and which gas sampling system includes an electrostatic precipitator constructed in accordance with another feature of this invention;

FIG. 2 is a vertical sectional view-through the electrostatic precipitator shown in FIG. 1 when taken as indicated by the arrows 2--2 of that Figure;

FIG. 3 is a vertical sectional view through the electrostatic precipitator of FIG. 2 when taken as indicated by the arrows 33 of that Figure;

FIG. 4 is a fragmentary vertical sectional view similar to that of FIG. 3 but when taken as indicated by the arrows 44 of FIG. 2; and

FIG. 5 is a horizontal sectional view through the electrostatic precipitator of FIGS. 2 to 4 when taken as indicated by the arrows 5-5 of FIG. 3.

Referring first to FIG. 1, there is indicated generally therein at a gas sampling system intended intermittently to withdraw gas samples from an ore reduction roaster generally indicated at 11 and to remove both coarse and finely divided particulate. solid material from such gas samples prior to passage of the resulting clean, dust-free gas samples to a gas chromatography unit generally indicated at 12 and having associated therewith in a conventional manner a sampling programmer 13 for controlling such gas chromatography unit so that it automatically carries out desired gas analyses after desired intervals of time.

It will be seen from FIG. 1 that the gas sampling system 10 includes a gas sampling line or conduit 14 which is connected by a coupling 15 to an opening (not shown) in a wall 16 of the ore reduction roaster 11. A

manually controlled gate valve 17 is provided in the gassampling line 14 for isolating the sampling system 10 from the roaster 11 when required.

A screen filter generally indicated at 18 which usefully includes a minus 325 mesh standard Tyler screen 19 clamped between circular flanges 20 and 21 of eccentric reducing couplings 22 and 23 respectively by bolts (not shown) is connected to the outer end of the sampling line 14 by means of the coupling 22. Gaskets (not shown) are usefully provided between the flanges 20 and 21 of the couplings 22 and 23 respectively to provide a gas-tight seal therebetween.

The reducing coupling 23 is in turn coupled to a transfer line or conduit 28 which includes a reducing coupling 29 and a smaller diameter downstream section 30 which leads to an electrostatic precipitator generally indicated at 31 and the construction of which will be described in greater detail as the description herein proceeds. A gas outlet line or conduit 32 extends from the electrostatic precipitator 31 to the aforementioned gas chromatography unit 12. From the latter, the gas is vented after analysis through a venting line 33.

With further reference to FIG. 1 of the accompanying drawings, it will be noted that, in accordance with a particularly important feature of this invention, a tee coupling 36 and a solenoid valve 37 are included in the transfer line 28 between the reducing couplings 23 and 29. A gas supply line 38 including a solenoid valve 39 is coupled to a leg of the tee coupling 36 and, for a purpose which will be more readily understood when the operation of thesystem 10 is described hereinafter, the solenoid valves 37 and 39 are operatively associated with the sampling programmer 13 of the gas chromatography unit 12 as indicated by the broken lines 40 and 41 respectively, so that the operation of such valves, i.e., their movement between open and closed positions, is automatically controlled by that programmer 13. The gas supply line 38 is adapted in any appropriate manner (not shown) to be coupled to a source of blow-back gas.

In the operation of the gas sampling system 10 with the gate valve 17 in its normal and operative open position, a gas sample from within the ore reduction roaster 11 passes through the sampling line 14 to the screen filter 18 in which the filter screen 19 is effective to remove dirt, sootand other coarse particulate material from that gas stream.

From the screen filter 18, the gas sample stream passes through the transfer line 28, the solenoid valve 37 and the reduced diameter conduit 30 to the electrostatic precipitator 31 which is designed to have a very high dust-collecting efficiency and in which practically all the finely divided particulate material remaining in the gas stream is removed therefrom. It will be understood that, during such passage of the sample gas stream through the electrostatic precipitator 31 to the gas chromatography unit 12 for analysis therein, the sampling programmer 13 of the gas chromatography unit 12 will be operative to hold the solenoid valve 37 in its open position and to hold the solenoid valve 39 in its closed position.

After the analysis of a gas sample by the gas chromatography unit 12 has been completed, the sampling programmer 13 of unit 12 is operative to move the solenoid valve 37 into its closed position and'to move the solenoid valve 39 into its open position. With the gas supply line 38 coupled to a source of an inert blowback gasysuch as nitrogen, the opening of solenoid valve 39 permits a reverse flow of blow-back gas through the gas supply conduit 38, the tee coupling 36, the screen filter 18 the gate valve 17, and the gas sampling line 14 into the roaster 11. Such reverse flow of blow-back gas through the screen filter 18 and the sampling line 14 is highly effective for clearing dirt, soot and other solid particulate material both from the filter screen 19 and from the conduit 14 and the associated couplings to prevent the filter and conduit from becom ing plugged during continued operation of the gas sampling system 10.

As already indicated, one' important feature of the gas sampling system shown in FIG. 1 of the accompanying drawings resides in the provision of the electrostatic precipitator 31 and the construction of which will now be described in greater detail with reference to the remaining figures of the accompanying drawings.

The electrostatic precipitator 3l comprises a closed, generally gas-tight, stainless steel removable housing generally indicated at 44 and formed from interconnected front and rear'walls 45 and 46 respectively, side walls 47 and 48 and a base or floor 49. Flanges 50 are provided along the outer upper edges of the walls 45, 46, 47 and 48.

Housing 44 is removably attached in a gas-tight manner to cover plate 51 by means of bolts 52 having heads which are tack welded to plate 51. The shanks of the bolts extend downwardly through plate 51 and through apertures in flanges 50. Housing 44 is held in position beside cover plate 51 by means of nuts 53. Thus by removal of nuts 53, housing 44 may be removed from plate 51 thereby exposing the interior of the housing and permitting the dust particles collected in the bottom of the housing to be removed.

Secured to the cover plate 51, for example, by welding, and extending downwardly therefrom into the housing 44, there is provided a stainless steel partition or septum plate 54 which downwardly terminates upwardly of the floor 49 so as to divide the housing 44 into a first or ionization chamber 55, a second or dustcollection chamber 56 and a third or collector chamber 57 as will readily be understood by reference to FIG. 2. As will be seen by reference to FIG. 5, the side edges of the partition 54 are slideable within vertically extending grooves or recesses 58 and 51 formed for this purpose in the side walls 47 and 48 respectively, hereby the housing may be removed by downward sliding following removal of nuts 53. In this way, the ionization chamber 55 and the collector chamber 57 are separated from each other for gas flow therebetween except through the dust-collection chamber 56. The direction of gas flow through the chambers 55, 56 and 57 is indicated by the arrows A in FIG. 2 of the drawings.

An ionization electrode in the form of a tightly stretched continuous chrome] DSA gauge wire generally indicated at 60 is mounted in the ionization chamber 55 as a plurality of vertically spaced apart and transversely extending stretches, the ends of each of which are clamped in insulator strips 61 which are in turn clamped to the partition 54 by bolts 62;

The upper end of the wire ionization electrode 60 is connected to the center electrode of a spark plug type feedthrough connector 63 screwed into an upstanding sleeve 64 suitably mounted on the cover plate 51. A tubular insulator 65 is provided around the upper end of the wire electrode 60 immediately below the cover plate 51. A high voltage supply cable 66 (shown fragmentarily in FIG. 2) is connected to the terminal of th spark plug type connector 63.

A collector plate electrode 67 is similarly mounted in the collector chamber 57 generally centrally therein and with the side edges of that electrode 67 received in generally vertical and opposed slots or recesses in insulator strips 68 which are also secured to the partition 54 by the aforementioned bolts 62 as will readily be understood by reference to FIG. 5 of the accompanying drawings. It will also be seen that the plate electrode 67 extends downwardly within the collector chamber 57 so that a lower edge 70 of that electrode is disposed in general proximity to the lower end of the collector chamber 57 and slightly upwardly of the dust collection chamber 56.

Electrical energy is supplied to the collector plate electrode 67 by a spark plug type connector 71 mounted in an internally threaded sleeve 72 extending through the cover plate 51. A center electrode 73 of the connector 71 is threaded into a connector 74 suitably secured, for example, by welding to the upper end of the collector plate electrode 67. An insulating, sleeve 75 is provided around the center electrode 73 and a high voltage supply cable 76 (omitted from FIG. 2) is connected to the terminal of the spark plug type connector 71.

In accordance with another useful feature of this invention, the spark plug type connectors 63 and 71 are enclosed within a generally gas-tight casing generally indicated at'77 and including side walls 78 and a top cover 79. The casing 77 is secured to the cover plate 51 by screws 80, a gasket 81 being provided to ensure a gas-tight seal. The open front and rear faces of the casing 77 are closed by removable panels 82 which are held in place by bolts 83, further gaskets being provided to ensure a gastight seal.

Electrical supply conduits 84 are secured in openings in the top cover 79 of the casing 77 in a conventional manner and the aforementioned cables 66 and 76 extend through these conduits 84 to a suitable high voltage electrical supply unit (not shown). An inert gas such as nitrogen is supplied into the casing 77 through one of the conduits 84 and exhaust therefrom through the other such conduit 84. In this way, protection of personnel against accidental electrical shock and safe operation of the electrostatic precipitator 31 in hazardous or flammable atmospheres are ensured.

A sample gas supply conduit 87 is connected by a fitting 88 in the aforementioned cover plate 51 for the supply of dust-laden gas into the ionization chamber 55 while the other end of the conduit 87 is suitably connected to a coupling 89 mounted in the side wall 78 of the casing 77, for connection, for example, to the end of the small diameter section 30 of the transfer conduit 28 shown in FIG. 1.

In a similar manner, a gas discharge line or conduit 90 is connected between a coupling 91 suitably mounted on the cover plate 51 and a coupling 92 mounted on the opposite side wall 78 of thecasing 77, for the discharge of the sample gas stream from the collector chamber 57 of the electrostatic precipitator 31 into the gas discharge conduit 32 shown in FIG. 1.

In the operation of the electrostatic precipitator 31, a gas ionizing electrical field is set up between the ionization wire electrode 60 and the walls of the ionization chamber 55, the required direct current potential being applied to the electrode 60 through the cable 66. On the flow of a gas stream through the electrostatic precipitator 31 as indicated by the arrows A, the ionized gas formed in the ionization chamber 55 serves to charge the dust particles contained therein and some of the resulting electrically charge dust particles are then attracted to the walls of the chamber 55.-

The smaller dust particles present in such a gas stream and which are not collected on the walls of the ionization chamber 55 flow downwardly through that chamber 55 with the gas stream which essentially reverses its direction of flow in passing from the ionization chamber 55 through the dust collection chamber 56 and into the collector chamber 57.

The collector chamber 57 is not ionizing and the electrode 67 and the walls of this chamber serve to attract and collect the remaining charged small particles. The dust collection chamber 56 functions to collect any solid material which falls from the chambers 55 and 57. The material may be removed by unscrewing nuts 50 and lowering housing 44 until it is clear of electrodes 60 and 67 and septum plate 54. The housing is then overturned in order to empty the material therefrom.

With the particular construction illustrated, the gas flow velocity through the dust collection chamber 56 is sufficiently low to prevent excessive dust pick-up by the gas stream flowing therethrough and, since the lower edge of the-collector electrode 67 is effective to ionize the gas stream flowing therepast, the particles of any dust so entrained in the gas stream are electrically charged and consequently collected on passage through the collector chamber 57.

The electrostatic precipitator shown in FIGS. 2 to 5 has proved to be particularly effective in removing finely divided particulate material remaining in a gas stream flowing from a screen filter such as the screen filter 18 shown in FIG. I and has been shown to have a high collection efficiency even for particles smaller than 0.0l microns in diameter so that the gas stream issuing from such an electrostatic precipitator can be considered to be essentially completely dust-free.

In the use of the electrostatic precipitator 31 shown in FIGS. 2 to 5 in the gas sampling system shown in FIG. 1, continued operation of that system is possible with practically no risk of plugging of the screen filter 18, the sampling line 14 or of dust contamination of the sampling tube of the gas chromatography unit 12 with dust particles.

What we claim as new and desire to protect by Letters Patent of the United States is:

1. A gas sampling system for the removal of solid particles from a gas stream sampled from an ore reduction roaster for passage to a gas'chromatography analysis unit, which system includes a sampling line adapted to be connected to such an ore reduction roaster for the passage through said sampling line of a gas stream laden with both coarse and finely divided solid particles a screen filter in said sampling line for the passage of said gas stream therethrough for the removal of coarse solid particles, from said gas stream by said filter; an electrostatic precipitator for the removal of finely divided solid particles from said gas stream flowing from said screen filter; a transfer line interconnecting said screen filter and said electrostatic precipitator for the passage of a gas stream from said screen filter, after the removal of coarse solid particles therefrom by said screen filter, to said electrostatic precipitator; a gas chromatography unit; gas outlet means interconnecting said electrostatic precipitator and said gas chromatography unit for the flow of a gas stream from said electrostatic precipitator, after the removal of said finely divided solid particles from such a gas stream in said electrostatic precipitator; first valve means operatively associated with said transfer line for movement between open and closed positions for controlling the flow of a gas stream through said transfer line to said electrostatic precipitator; a gas supply line in gaseous communication with said transfer lineupstream of said first valve means for the introduction into said transfer line of a blow-back gas; and second valve means operatively associated with said gas supply line for movement between open and closed positions for permitting the flow of blow-back gas when in said open position thereof through said gas supply line into said transfer line and, when in said closed position thereof, for preventing the flow of said gas stream from said screen filter into said gas supply line, whereby said gas sampling system may be used with said first valve means in said open position thereof and with said second valve means in said closed position thereof to remove both coarse and finely divided solid particles from a gas stream sampled from an ore reduction roaster and to supply the resultingly cleaned gas stream through said gas outlet means to said gas chromatography unit, and whereby a blow-back gas may be introduced into said system through said gas supply line with said second valve means in said open position thereof and with said first valve means in said closed position to cause a reverse flow of gas through a part of said transfer line to said screen filter and then through said sampling line to dislodge solid particles from within said transfer and sampling lines and from said screen filter and to return resultingly dislodged solid particles to said reduction roaster; a sampling programmer for effecting intermittent analysis of gas samples supplied thereto and in which said first and second valve means are adapted to be operatively connected to such s sampling programmer for the control and automatic operation of said first and second valve means by such a sampling programmer for blow-back operation between successive analyses, said electrostatic precipitator comprising a closed housing with electrically conductive side walls and internally divided into an ionization chamber and a collector chamber by a partition extending downwardly into said housing but terminating upwardly of a floor of said housing to provide a dust collection chamber disposed downwardly of said ionization chamber and said collector chamber and through which said ionization chamber and said collector chamber are in gaseous communication with each other; an ionization electrode mounted in said ionization chamber on electrically insulating support means and comprising a wire formed into a plurality of interconnected stretches disposed transversely to the downward gas flow through said ionization chamber for gas flow around each said stretch of said wire; gas inlet means connected to said transfer line andcommunicating with said ionization chamber for thepassage of a gas stream from said transfer line into said ionization chamber for downward flow therethrough into said dust collection chamber; high voltage electrical supply means electrically connected to said ionization electrode for the application thereto of a high electrical voltage relative to said electrically conductive side walls of said housing whereby electrical discharge from said ionization electrode causes dust particles in a gas stream flowing 7 through said ionization chamber to become electrically charged; a collector electrode mounted in said collec-' tor chamber on electrically insulated support means and comprising a plate extending upwardly within said collector chamber for the passage of a gas stream along both faces thereof and having a lower edge disposed upwardly of said dust collection chamber and transversely to the gas'flow from said dust collection chamber into said collector chamber and operative to cause additional electrical discharge into such a gas stream; high voltage electrical supply means electrically connected to said collector electrode for the application thereto of a high electrical voltage relative to said electrically conductive side walls of said housing; gas outlet means communicating with said collector chamber for the passage therefrom to a gas chromatography unit of a gas stream flowing from said dust collection chamber upwardly through said collector chamber, whereby electrically charged dust particlespresent in said gas stream flowing upwardly through said collector chamber are attracted to and collected on said collector electrode and a respective one of said electrically conductive side walls of said housing and whereby a gas stream flowing from a transfer line through said electrostatic precipitator must undergo a reversal of flow direction within said electrostatic precipitator in passing out of said ionization chamber through said dust collection chamber and chamber thereof; said housing further including a cover plate detachably secured in a generally gastight manner to said side walls, in which said ionization electrode and said collector electrode of said electrostatic precipitator are mounted by respective ones of said electrically insulating support means which are in turn mounted on said partition and which is in turn secured to said cover plate whereby said partition and said electrodes of said electrostatic precipitator may readily be r removed from within said housing thereof by detaching said cover plate from said side walls of said housing and withdrawing said partition and said electrodes from within said housing, in which each said high voltage electrical supply means of said electrostatic precipitator comprises an electrical terminal mounted on said cover plate and extending therethrough into a respective one of said ionization chamber and said collector chamber, which housing additionally includes a generally gas-tight casing detachably secured thereto about said electrical terminals outwardly of said cover plate, and in which electrostatic precipitator gas flow means are provided for the su ply and discharge of an inert gas into and out of said gas-tlght casing of said electrostatic precipitator, said gas inlet and gas outlet means commencing at said ionization chamber and said collector chamber respectively, extending through said casing and terminating at said side wall.

into said collector- 

1. A gas sampling system for the removal of solid particles from a gas stream sampled from an ore reduction roaster for passage to a gas chromatography analysis unit, which system includes a sampling line adapted to be connected to such an ore reduction roaster for the passage through said sampling line of a gas stream laden with both coarse and finely divided solid particles a screen filter in said sampling line for the passage of said gas stream therethrough for the removal of coarse solid particles from said gas stream by said filter; an electrostatic precipitator for the removal of finely divided solid particles from said gas stream flowing from said screen filter; a transfer line interconnecting said screen filter and said electrostatic precipitator for the passage of a gas stream from said screen filter, after the removal of coarse solid particles therefrom by said screen filter, to said electrostatic precipitator; a gas chromatography unit; gas outlet means interconnecting said electrostatic precipitator and said gas chromatography unit for the flow of a gas stream from said electrostatic precipitator, after the removal of said finely divided solid particles from such a gas stream in said electrostatic precipitator; first valve means operatively associated with said transfer line for movement between open and closed positions for controlling the flow of a gas stream through said transfer line to said electrostatic precipitator; a gas supply line in gaseous communication with said transfer line upstream of said first valve means for the introduction into said transfer line of a blow-back gas; and second valve means operatively associated with said gas supply line for movement between open and closed positions for permitting the flow of blow-back gas when in said open position thereof through said gas supply line into said transfer line and, when in said closed position thereof, for preventing the flow of said gas stream froM said screen filter into said gas supply line, whereby said gas sampling system may be used with said first valve means in said open position thereof and with said second valve means in said closed position thereof to remove both coarse and finely divided solid particles from a gas stream sampled from an ore reduction roaster and to supply the resultingly cleaned gas stream through said gas outlet means to said gas chromatography unit, and whereby a blow-back gas may be introduced into said system through said gas supply line with said second valve means in said open position thereof and with said first valve means in said closed position to cause a reverse flow of gas through a part of said transfer line to said screen filter and then through said sampling line to dislodge solid particles from within said transfer and sampling lines and from said screen filter and to return resultingly dislodged solid particles to said reduction roaster; a sampling programmer for effecting intermittent analysis of gas samples supplied thereto and in which said first and second valve means are adapted to be operatively connected to such s sampling programmer for the control and automatic operation of said first and second valve means by such a sampling programmer for blow-back operation between successive analyses, said electrostatic precipitator comprising a closed housing with electrically conductive side walls and internally divided into an ionization chamber and a collector chamber by a partition extending downwardly into said housing but terminating upwardly of a floor of said housing to provide a dust collection chamber disposed downwardly of said ionization chamber and said collector chamber and through which said ionization chamber and said collector chamber are in gaseous communication with each other; an ionization electrode mounted in said ionization chamber on electrically insulating support means and comprising a wire formed into a plurality of interconnected stretches disposed transversely to the downward gas flow through said ionization chamber for gas flow around each said stretch of said wire; gas inlet means connected to said transfer line and communicating with said ionization chamber for the passage of a gas stream from said transfer line into said ionization chamber for downward flow therethrough into said dust collection chamber; high voltage electrical supply means electrically connected to said ionization electrode for the application thereto of a high electrical voltage relative to said electrically conductive side walls of said housing whereby electrical discharge from said ionization electrode causes dust particles in a gas stream flowing through said ionization chamber to become electrically charged; a collector electrode mounted in said collector chamber on electrically insulated support means and comprising a plate extending upwardly within said collector chamber for the passage of a gas stream along both faces thereof and having a lower edge disposed upwardly of said dust collection chamber and transversely to the gas flow from said dust collection chamber into said collector chamber and operative to cause additional electrical discharge into such a gas stream; high voltage electrical supply means electrically connected to said collector electrode for the application thereto of a high electrical voltage relative to said electrically conductive side walls of said housing; gas outlet means communicating with said collector chamber for the passage therefrom to a gas chromatography unit of a gas stream flowing from said dust collection chamber upwardly through said collector chamber, whereby electrically charged dust particles present in said gas stream flowing upwardly through said collector chamber are attracted to and collected on said collector electrode and a respective one of said electrically conductive side walls of said housing and whereby a gas stream flowing from a transfer line through said electrostatic precipitator must undergo a reversal of flow direction within Said electrostatic precipitator in passing out of said ionization chamber through said dust collection chamber and into said collector chamber thereof; said housing further including a cover plate detachably secured in a generally gas-tight manner to said side walls, in which said ionization electrode and said collector electrode of said electrostatic precipitator are mounted by respective ones of said electrically insulating support means which are in turn mounted on said partition and which is in turn secured to said cover plate whereby said partition and said electrodes of said electrostatic precipitator may readily be removed from within said housing thereof by detaching said cover plate from said side walls of said housing and withdrawing said partition and said electrodes from within said housing, in which each said high voltage electrical supply means of said electrostatic precipitator comprises an electrical terminal mounted on said cover plate and extending therethrough into a respective one of said ionization chamber and said collector chamber, which housing additionally includes a generally gastight casing detachably secured thereto about said electrical terminals outwardly of said cover plate, and in which electrostatic precipitator gas flow means are provided for the supply and discharge of an inert gas into and out of said gastight casing of said electrostatic precipitator, said gas inlet and gas outlet means commencing at said ionization chamber and said collector chamber respectively, extending through said casing and terminating at said side wall. 